Avalanche Forecast

Issued: Dec 4th, 2012 9:01AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Wind Slabs, Storm Slabs and Persistent Slabs.

ccampbell, Avalanche Canada

South Coast.

Summary

Confidence

Fair - Due to limited field observations for the entire period

Weather Forecast

Wednesday: Moderate snowfall with 5010cm of accumulation, freezing levels around 700m, and strong southwesterly winds easing throughout the day. Thursday: Moderate snowfall with another 5-10cm of accumulation, or more in the Coquihalla Pass area, freezing levels rising to 800m, or higher in Coquihalla Pass, and moderate southwesterly winds. Friday: Light snowfall with up to 5cm of accumulation freezing levels in valley bottoms but rising throughout the day, and moderate southwesterly winds.

Avalanche Summary

No new avalanche observations have been reported; however, heavy loading from snow and wind on Tuesday likely resulted in natural avalanche activity, particularly on leeward slopes.

Snowpack Summary

The Coquihalla Pass area received 90cm of new snow since Sunday, while the Duffy Lake area got about 50cm. Weaknesses linger within and under this storm snow. Of particular note is surface hoar buried late last week, which is likely well preserved and weak on sheltered open slopes treeline and below. The mid-pack seems to be well settled and strong, and possibly bridging deeper weaknesses. However, it wasn't too long ago when snowpack tests were producing moderate but sudden collapse results on the early November facet/crust combination near the base of the snowpack. Furthermore, favorable slab structure for step-down fractures can contribute to the persistence of this deep weakness.

Problems

Wind Slabs

Fresh wind slabs can be found well below ridge crests, behind terrain features and in cross-loaded gullies in any wind-exposed terrain. Expect these deep drifts to be very touchy.

Avoid freshly wind loaded features.>Give cornices a wide berth when travelling on or below ridges.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 5

Storm Slabs

Weaknesses within and under the recent storm snow are susceptible to human and natural triggers and could easily produce avalanches large enough to bury a person.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 5

Persistent Slabs

An old facet/crust combination deep in the snowpack may wake up with heavy triggers, smaller avalanches stepping down, or triggering from thin-spots, particularly on slopes with smooth ground cover.

Avoid convexities or areas with a thin or variable snowpack.>Be aware of thin areas that may propagate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Dec 5th, 2012 2:00PM